Valve actuating mechanism for an internal combustion engine

ABSTRACT

A valve actuating mechanism for the inlet valves E of a cylinder of an internal combustion engine has a first set of rocker arms 6 each of which actuates an inlet valve E and is actuated by a cam 2, 3, 4 for a lower engine speed range, and a second set of rocker arms 9 which are mounted between a first set of adjacent rocker arms 6 and are actuated by identical cams 8 for the higher engine speed range. The second set of rocker arms 9 is interconnected by means of a crosspiece 10. The first set of rocker arms 6 contains radially movable pistons 12 which in the higher speed range are displaced outward by oil pressure and against which the crosspiece 10 of the second set of rocker arms 9 can rest. Consequently, the valves E are actuated by the second set of rocker arms 9 as determined by the outline of the cams 8.

The invention relates to a valve actuating mechanism for an internalcombustion engine.

BACKGROUND OF THE INVENTION

In a state-of-the-art valve actuating mechanism of this type (EP-A 213759 or GB-A-2199894) connection between the first and the second set ofrocker arms in the higher speed range is effected by means of pistonsdisplaceable by oil pressure which are mounted radially to the swivelaxis of the rocker arms in bores provided in the rocker arms. The boresare aligned with each other when the rocker arms rest on the basecircles of their cams. In the lower speed range, in which the valves areto be actuated by the cams associated with the first set of rocker arms,the frontal surfaces of the meeting pistons are situated in the divisionplanes between the rocker arms, so that the valves are actuatedexclusively by the first set of rocker arms and the second set of rockerarms can swing freely. In the upper speed range the pistons aredisplaced in such a way that they penetrate the division planes, withthe result that the second set of rocker arms is connected to the firstset of rocker arms and the valves are actuated by the second set ofrocker arms as determined by the outline of the cams associated with thesecond set of rocker arms. Different valve lifts and different openperiods can accordingly be produced in the higher and the lower speedranges. One disadvantage of the state-of-the-art design is that in thelower speed range the frontal surfaces of the pistons continually slideinto each other and that very high precision is required in manufactureof the pistons and the bores.

SUMMARY OF THE INVENTION

It is an object of the invention to create a valve actuating mechanismof the state-of-the-art type in which wear is reduced and themanufacture of which is simplified.

It is proposed on the basis of the invention that the pistons beretained by springs in the lower speed range so that no contact takesplace with the second set of rocker arms. Since no bores are provided inthe second set of rocker arms that must come into alignment with thebores in the first set of rocker arms if the valves of the first set ofrocker arms are to be actuated by the second set of rocker arms,manufacture is significantly simplified. End facing of the bottom of thecrosspiece is all that is required.

Because of manufacturing considerations, the bores and the pistons inthe first set of rocker arms are preferably circular in cross-section.The end sections of the pistons, which in the higher speed range operatein conjunction with the bottom of the crosspiece, have a plane surface,as a result of which two-dimensional contact between piston andcrosspiece is effected and the surface pressure is correspondinglyreduced. In order to make certain that the plane surfaces of the endsections are at all times positioned parallel to the bottom of thecrosspiece, it is preferable to provide protection against rotation ofthe piston that can simultaneously limit the outward movement of thepiston.

BRIEF DESCRIPTION OF THE DRAWINGS

An example of an embodiment of the invention is described as followswith reference to the drawings, in which:

FIG. 1 shows a valve drive with a valve actuating mechanism inaccordance with the present invention for three inlet valves, in thevertical section along line 1--1 in FIG. 2, and

FIG. 2 presents a view in the direction of arrow 2 in FIG. 1.

DETAILED DESCRIPTION

A valve drive for three inlet valves E is shown in the drawings. Aspring 1 applies pressure to each valve E in the direction of closing.The valves are actuated by cams 2, 3, and 4 of a camshaft 5 by way of afirst set of rocker arms 6 rotatably mounted on a common stationaryshaft 7. The cams 2, 3, and 4 preferably have different cam profiles soas to achieve a different valve lift for the individual inlet valves, adifferent open period, and/or different control times in order toachieve optimum preliminary conditions in the lower and medium speedranges of the internal combustion engine. Mounted between adjacent cams2, 3, 4 on the camshaft 5 is a second set of cams 8 with an identicalcam profile designed for the conditions in the higher speed range of theinternal combustion engine, and this set accordingly effects, forexample, a greater valve lift and a longer open period. Operating inconjunction with the second set of cams 8 is a second set of rocker arms9 which may be coupled with the first set of rocker arms 6 in the higherspeed range, so that in this speed range the valves E are actuated asdetermined by the profile of the second set of cams 8. The free ends ofthe second set of rocker arms 9 are connected by a crosspiece 10 thatextends to the front of and a short distance from the free end of thefirst set of rocker arms 6. Radial bores 11 radial to the swivel axis ofshaft 7 are provided in the first set of rocker arms 6, in each of suchbores 11 a piston 12 is mounted that can be displaced between a firstinner position and a second outer position in which the piston projectsfrom its rocker arm 6. In this second position, shown in FIG. 1, thepistons 12 operate in conjunction with the flat bottom 10a of thecrosspiece 10, so that the second set of rocker arms 9 can actuate thevalves E by way of the first set of rocker arms 6 as determined by theoutline of the cams 8. Outward displacement of the pistons 12 iseffected by oil pressure introduced through a duct 14 in the shaft 7which communicates with the bores 11. If delivery of the pressure meansis interrupted, the pistons 12 are returned to their bores 11 by aspring 13, so that the second set of rocker arms 9 can pivot freely andthe valves are actuated by the first set of rocker arms 6 as determinedby the outline of the cams 2, 3, or 4. On one side the spring 13 restson an insert 15 fastened in bore 11 and on the other side the end of asleeve 16 that is fastened on the piston 12 and extends through theinsert 15.

Each rocker arm 6 or 9 has a sliding surface 17 by means of which therocker arm is applied to its cam 2, 3, 4, or 8. The second set of rockerarms 9 are kept applied at all times to their cams by a spring 18. Inthe exemplary embodiment the spring is mounted on a spark plug and restson one side on a stationary spring retainer and on the other on amovable spring retainer 21 that operates in conjunciton with extensions22 which partly encompass the spark plug dome.

The end sections of the pistons 12 are provided with plane surfacesagainst which rests the flat bottom 10a of the crosspiece 10 when thepistons 12 are in the extended position illustrated. The surfacepressure between the crosspiece 10 and the pistons 13 is accordinglyreduced. In order to avoid rotation of the pistons 12 and to makecertain that the plane surface 23 is at all times parallel to the bottom10a of the crosspiece, protection against rotation is provided in theform of a pin 24 that is inserted into the rocker arms 6 and whosefrontal surface rests against the plane surface 23 of the piston. In theextended position the shoulder 25 created by the plane surface 23 restsagainst the pin 24, as a result of which the outward movement of thepiston 12 is limited.

I claim:
 1. A valve actuating mechanism for an internal combustionengine including:at least two inlet valves (E) per cylinder; a first setof rocker arms (6) and a common shaft (7) for rotatively supporting saidfirst set of rocker arms, a camshaft (5) including first cams (2, 3, or4) and wherein each of said rocker arms of said first set operates inconjunction with an inlet valve and a first cam for a first engine speedrange; a second set of rocker arms (9) each of which is mounted betweentwo adjacent rocker arms of said first set (6), said common shaft (7)rotatively supporting said rocker arms of said second set, second cams(8), and wherein each of said rocker arms of said second set operates inconjunction with said second cams for a second engine speed range; aspring (18) for maintaining said second set of rocker arms against saidsecond cams (8); pistons (12) for coupling said first set of rocker armsto said second set of rocker arms in said second engine speed range;said first set of rocker arms including a plurality of bores (11) foraccommodating said pistons, said bores extending radially to said commonshaft and said pistons being movable outward in said bores by oilpressure, and springs (13) for opposing said outward movement of saidpistons; said second set of rocker arms including free ends, and acrosspiece (10) for connecting together said free ends, said first setof rocker arms including free ends and said crosspiece being positionedin front of said first rocker arm free ends; and said crosspieceincluding a flat bottom (10a) for cooperating with said pistons whensaid pistons are displaced outward.
 2. A valve actuating mechanism as inclaim 1 wherein said pistons have a circular cross section and includeends provided with a plane surface (23) for cooperation with saidcrosspiece flat bottom when said pistons are displaced outward.
 3. Avalve actuating mechanism as in claim 2 including means for preventingrotation and limiting outward movement of said pistons.
 4. A valveactuating mechanism as in one of claims 1, 2, or 3 wherein said commonshaft includes an oil delivery duct (14) in communication with saidbores (11) of said first set of rocker arms.